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i2c: fix different frequency duty according to I2C-BUS spec

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PD#164083: i2c: fix duty of different frequency

1.General usage
Frequency   Duty    mode

100k	    1:2	    standard
400k	    1:3	    fast
3400k	    1:3	    high

2.Frequency below 100k can be configured as fast mode

Change-Id: Ib6254efabfbd614c014c98bbeb3d07c35cf7b904
Signed-off-by: Jian Hu <jian.hu@amlogic.com>
This commit is contained in:
Jian Hu
2018-04-11 16:11:55 +08:00
committed by Yixun Lan
parent d4ca0fee7e
commit d363baac44
1 changed files with 22 additions and 11 deletions
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33
drivers/amlogic/i2c/i2c-meson-master.c
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@@ -91,6 +91,7 @@ struct meson_i2c_data {
* @frequency: Operating frequency of I2C bus clock
* @tokens: Sequence of tokens to be written to the device
* @num_tokens: Number of tokens
* @retain_fast_mode: low frequency using high mode,for less than 100k
*/
struct meson_i2c {
struct i2c_adapter adap;
@@ -112,6 +113,7 @@ struct meson_i2c {
u32 tokens[2];
int num_tokens;
int retain_fastmode;
struct meson_i2c_data *data;
};
@@ -150,12 +152,6 @@ static void meson_i2c_write_tokens(struct meson_i2c *i2c)
}
/*
* According to I2C-BUS Spec 2.1, in FAST-MODE, LOW period should be at
* least 1.3uS, and HIGH period should be at lease 0.6. HIGH to LOW
* ratio as 1 to 2 is more safe.
*
* So in FAST-MODE, we should control the SCL low time.
*
* Count = clk/freq = H + L
* Duty = H/(H + L) = 1/2 -- duty 50%
* H = n + delay
@@ -165,8 +161,9 @@ static void meson_i2c_write_tokens(struct meson_i2c *i2c)
*
* n = Count/2 - delay
* m = Count/4
* Standard Mode : 100k
*/
static void meson_i2c_set_clk_div_fast(struct meson_i2c *i2c)
static void meson_i2c_set_clk_div_std(struct meson_i2c *i2c)
{
unsigned long clk_rate = clk_get_rate(i2c->clk);
unsigned int div_h, div_l;
@@ -207,7 +204,15 @@ static void meson_i2c_set_clk_div_fast(struct meson_i2c *i2c)
__func__, clk_rate, i2c->frequency, div_h, div_l);
}
static void meson_i2c_set_clk_div_std(struct meson_i2c *i2c)
/*
* According to I2C-BUS Spec 2.1, in FAST-MODE, LOW period should be at
* least 1.3uS, and HIGH period should be at lease 0.6. HIGH to LOW
* ratio as 1 to 2 is more safe.
* Duty = H/(H + L) = 1/3 -- duty 33% H/L = 1/2
* Fast Mode : 400k
* High Mode : 3400k
*/
static void meson_i2c_set_clk_div_fast(struct meson_i2c *i2c)
{
unsigned long clk_rate = clk_get_rate(i2c->clk);
unsigned int div;
@@ -236,10 +241,13 @@ static void meson_i2c_set_clk_div_std(struct meson_i2c *i2c)
static void meson_i2c_set_clk_div(struct meson_i2c *i2c)
{
if (i2c->frequency > 100000) {
if (i2c->frequency >= 400000)
meson_i2c_set_clk_div_fast(i2c);
} else {
meson_i2c_set_clk_div_std(i2c);
else {
if (!i2c->retain_fastmode)
meson_i2c_set_clk_div_std(i2c);
else
meson_i2c_set_clk_div_fast(i2c);
}
}
@@ -499,6 +507,9 @@ static int meson_i2c_probe(struct platform_device *pdev)
&i2c->frequency))
i2c->frequency = DEFAULT_FREQ;
if (fwnode_property_present(&np->fwnode, "retain-fast-mode"))
i2c->retain_fastmode = 1;
i2c->dev = &pdev->dev;
platform_set_drvdata(pdev, i2c);